1. Field of the Invention
The invention relates to an electrical terminal, especially a high current terminal, with a strain relief device.
2. Description of Related Art
Electrical terminals with contact elements made as tension springs, often called tension spring terminals, have been used for decades in industrial connection technology. In addition, electrical terminals with a screw-type terminal have been used for decades. The clamping principle for tension spring terminals is similar to that of screw technology. While in screw-type terminals a tension sleeve pulls the lead against a conductor bar by actuating the clamping screw, for a tension spring terminal this task can be assumed by a tension spring bent into a loop shape. The pretensioned tension spring is opened with an actuating tool, such as a screwdriver, so that the lead can be inserted into a through opening in the clamping leg of the tension spring into the terminal space. After removing the actuating tool, the lead is pulled by spring force against the conductor bar, which adjoins the contact leg of the tension spring.
One modification of the above described tension spring terminals is represented by electrical terminals with at least one strain-relief clamp connection as a spring force clamping terminal. With these electrical terminals, based on the special configuration of the strain-relief clamp connection, electric leads with a relatively large cross section of preferably 35 mm2 to 150 mm2 can be connected. In contrast, generally leads with cross sections of 1.5 mm2, 2.5 mm2, 4 mm2, 6 mm2, and 10 mm2 to 35 mm2, and those with special configurations, are connected to “normal” tension spring terminals. Since higher currents can be transmitted via electric leads with a larger cross section, electrical terminals made for connecting to leads with a large cross section are often also called high current terminals.
High current terminals are made both with a screw-type terminal and with a spring force clamping terminal. The high clamping forces of the screw-type terminal or spring force clamping terminal are achieved in the prior art by the respective clamping terminals, i.e. the contact element, which is designed to be thicker, extending from the electrical terminals for connection of “normal” leads. However, since high current terminals must also be manually actuated for opening the clamping sites against the respective clamping force of the clamping terminal, maximization of the type of construction of conventional terminals is limited, since lead cross sections starting with 50 mm2 often require excessive handling forces.
Electrical terminals for use as high current terminals have been developed that have strain-relief clamp connections, which consist of a generally U-shaped strain-relief clamp and a compression spring. The compression spring is located in the strain-relief clamp such that it pulls or biases the bottom end of the strain-relief clamp against the bottom of a conductor bar that extends through openings in the clamping leg of the strain relief clamp. By this, an electric lead inserted through the through opening in the clamping leg of the strain-relief clamp is clamped fast against the bottom of the conductor bar. In electrical terminals designed for leads with large cross sections, the clamping site of this strain-relief clamp connection, for which the compression spring must be axially compressed, can only be opened using support measures.
One known electrical terminal is disclosed in DE 198 17 924 C2. In this high current terminal, the actuating element for opening and closing the strain-relief clamp connection is a feed rotation cylinder, which is supported in the insulating housing above the strain-relief clamp and coaxially with the compression spring of the strain-relief clamp connection. The rotation cylinder has an outside thread so that it can be screwed into an inside thread formed on the insulating housing by means of a rotary tool that can be axially inserted into the cylinder. When the feed rotation cylinder is screwed in, the strain-relief clamp is pressed against the compression spring. The compression spring is thus compressed, by which the strain-relief clamp connection is opened so that an electric lead to be connected can be inserted between the lower edge of the through opening in the clamping leg of the tension spring and the conductor bar.
When using compression springs with high spring force, the execution of the feed rotation cylinder allows the clamping site to be manually opened without great expenditure of force. However, the configuration of the feed rotation cylinder and the inside thread in the insulating housing of the terminal are relatively complex and thus expensive to manufacture.